1. Field of the Invention
This invention relates to dental reconstruction and more specifically to methods and guides to describe aesthetic components of natural teeth with multidimensional descriptors representing aesthetic features of a tooth useful in reconstructive dentistry.
2. Prior Art
It is common for manufacturers of tooth prostheses to provide samples of multi-colored fabricated teeth as a shade guide for comparison with a patient""s teeth to determine tooth color shade and color saturation. The dentist then communicates that color shade and saturation to a dental laboratory and the dental laboratory creates a tooth as described. Unfortunately, the new replacement tooth or crown often does not match the patients mouth, frustrating the patient, the dentist, and the laboratory technician. Perhaps the most frustrating and disappointing element in tooth reconstruction is a restoration that doesn""t blend with surrounding natural teeth. With advances in ceramic technology, disappointing results are not for lack of capability to reproduce teeth but more so in the approach to measuring and communicating tooth appearance between an observer, typically in a dental office, and a reconstructive technician, typically in a dental laboratory.
For the past fifty years or so the standard communication for the appearance of tooth structure has been color. Hue describes the general color group of a tooth, a characteristic established at birth. Chroma is the saturation of color within that hue color group. Dental offices have attempted to describe a tooth to a dental laboratory by referring to a standard tab in a shade guide, comparing a tooth to those in the guide to locate the most similar hue and saturation. Hue and chroma have been represented in tab form from the shade guide to represent first the correct color group (hue) and then the proper amount of color saturation (chroma). Certainly color and hue are important components to tooth description, but alone they are not adequate. There are additional and important tooth characteristics that also require communication to the reconstructive technician. Additional variables are required, including optical density and brightness. Optical Density means the translucency of the tooth, the degree light is reflected or transmitted. Value is the brightness of the tooth.
About ten years ago, some technicians began including value as a second element of tooth description. By adding value as a descriptor, a tooth could be described not only as having a certain color and amount of color within a color shade, but it could also be described by how bright the tooth was. By simply adding a value rating to a tooth prescription, one gains good predictability about how the final crown will appear. Value is, in fact, as important as hue and chroma when one wants a crown to disappear and blend in.
Though hue and color have been the traditional descriptors for many years, and recently value, or brightness, has been added by some dental professionals, perhaps the most important factor in dental ceramics is optical density, or translucencyxe2x80x94the passage of light through different parts of a crown. It is now recognized that the most visibly offensive restorations fail to display the depth, translucency and vitality of natural teeth. Crowns that ignore translucency don""t blend in with the surrounding dentition; they attract too much attention in all lighting conditions irrespective of color group or saturation. One might consider two teeth displaying the same hue and chroma and the same value or brightness, yet one may have a very chaulky appearance and the other may have a very glassy look. To describe these two teeth with the use of only value and hue and chroma is nearly impossible; they would have the same prescription. The defining visual difference is translucency, the ability of a tooth to transmit light, which can be independent of value and also independent of chroma and hue. Optical density must be utilized to allow a description of a glassy or chalky tooth and must be recognized as an additional dimension in the description of the visual appearance of teeth.
The significant advances in dental porcelain have been the changes in the optical qualities of the material. One of the first optical improvements was fluorescence. Ultraviolet light interacts with materials causing them to fluoresce and emit a bright, visible whitish light. The inclusion of fluorescent material in dental porcelain enabled it to brighten in sunlight and UV light conditions similar to natural teeth, eliminating noticeable value changes.
Another advance in ceramics has been opalescence, an optical property that controls the passage of light by the size of its wavelength. Microfine particles are incorporated into porcelain to scatter and reflect blue wavelengths in direct light and allow longer orange wavelengths to pass through in indirect lighting conditions. Hydroxyapatite crystals in natural teeth are similar size (0.02 to 0.04 microns) and give teeth natural opalescence.
Opalescence in teeth is especially visible in the anterior region. Anteriors can be subject to both direct and indirect lighting as opposed to posteriors that we view in direct light only. As a result, this opal affect is primarily used in incisal or enamel powders.
Although the bluish and orange effects contribute to the realism of a restoration, the more practical advantage of opal incisal is the control of brightness. Before opalescence was introduced into dental porcelain, increased translucency meant increased grayness and lower value. Opalescing particles raise the refractive index of light due to their interaction with light, both by scattering and reflecting light waves. This higher refractive index allows the laboratory to produce a bright, beautiful translucency that will not gray in the oral environment.
This advancement was the key to controlling value and translucency independently. Using a complex selection of body porcelain, incisals, and modifiers several levels of opacity or translucency can be constructed. Layering these porcelains in different combination controls passage of light even in different parts of a crown as necessary to correctly reproduce an original tooth, blocking the passage of light by reflecting it or selectively scattering and diffusing it or alternately allowing it to pass and transmit through the structure, producing an appearance of a natural tooth.
With the recognition that in order to adequately describe a tooth, translucency and value must be described in addition to hue and chroma. What is needed now is a process of simply and logically communicating characteristics of a natural tooth between a dental office and a dental laboratory, a method coordinated to the changes in modern dental porcelain systems yet familiar to the dental office and inexpensive so dental offices will be inclined to readily incorporate the process.
These objects are achieved in a dental aesthetic guide that incorporates these several descriptors of translucency, brightness, hue and chroma to represent a patient""s appearance.
A tooth characterization guide allows a dentist to compare additional guide samples in value and translucency with a patient""s mouth in the method similar to that previously used by dentists in obtaining hue and chroma of a tooth. From these tooth samples the dentist is able to first choose a suitable translucency, which is the most important and influential factor for true tooth replication from a first set of samples. The dentist then is able to choose a suitable brightness from a second set of samples. The dentist then is able to choose a suitable color and saturation from a third set of samples. Typically, the dentist is able to use his set of samples of hue and chroma that he is already familiar with using. If desired, additional anterior tooth characteristics may also be selected, including a cracking, check lines, spotting, banding, staining, white hallo and orange hallo.